US6958865B1 - Microlicensing particles and applications - Google Patents

Abstract

A microscopic lens, of size approximately 1 micron is used for its optical characteristics.

Description

RELATED APPLICATIONS

This application is a Division of 09/441,152 Nov. 12, 1999 now U.S. Pat. No. 6,614,598 which claims the benefit of the U.S. Provisional Application No. 60/108,385, filed on Nov. 12, 1998.

GOVERNMENT CONTRACTS

The work described in this application was supported by Grant No. PHY97-22417 awarded by the National Science Foundation.

BACKGROUND

Spherical polymer microspheres can be mass produced with extraordinary precision and low cost. Many uses for these microspheres have been developed that rely on the specific binding of a microsphere to a target, and the labelling of the polymer microsphere with various dyes or magnetic material.

Spherical glass lenses greater than 1 mm in diameter are used for coupling light into or out of fibers as well as for relaying images across a short distance.

The present application describes new optical applications of spherical polymer microspheres less than 10 microns in diameter.

SUMMARY

The present application teaches a special microlensing particle and applications of the particle. According to the present invention, a latex microsphere of diameter 0.3 μm-4 μm is obtained. Latex microspheres of this type are commercially available and have been used in pregnancy tests and other applications that do not exploit their optical properties.

According to the present system, the latex microsphere is preferably less than 10 μm in diameter, more preferably 1 to 2 μm in diameter. The latex microsphere is used in combination with an optical imaging element.

Applications of the latex microsphere include a micro lensing rotational probe for use in detecting high frequency rotational motion, a scanning microscope, and a diode laser collimator device.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects will now be described in detail with respect to the accompanying drawings, wherein:

FIG. 1 shows a diagram of the optical microsphere;

FIG. 2A shows optical ray tracing of dual microspheres;

FIG. 2B shows the microspheres arranged in an enhanced signal mode;

FIGS. 2C and 2D shows schematic views illustrating the magnitude of the signal received based upon orientation of the microspheres ofFIGS. 2A and 2B, respectively.

FIG. 3 shows a block diagram of the electronics used in the rotation detector;

FIG. 4 shows an optical microscope formed with a microsphere lens;

FIG. 5 shows a laser with a microsphere lens;

FIG. 6 shows a fiber with a microsphere lens.

DETAILED DESCRIPTION

FIG. 1 shows the use of a miniature optical element, e.g., a spheroid element, e.g. a microsphere, to change the characteristics of incoming light. Theoptical microsphere100 is a latex sphere or spheroid body, which has at least one round cross section, and in which the diameter D of the round cross section is between 0.8 and 2 um. More generally, the Latex particles of this type are commercially available from Bangs, or Interfacial Dynamics Corporation, or other companies.

It was found by the present inventors that the latex sphere has a collimating effect on incoming light. Incominglight110 is collimated by the sphere into collimatedlight120. The collimated light can be used for various purposes described herein.

A first embodiment is used to sense high frequency rotational motion. An asymmetric fluorescent probe is formed of amicrosphere pair199 as shown in FIG.2A. The probe includes afirst latex microsphere200 in optical and physical contact with asecond latex microsphere210. Thefirst microsphere200 is approximately 1.1 μm in diameter and forms a lensing portion. Thesmaller microsphere210, which can be between 0.5 um and 1 um, is fluorescently-labeled. Thelarger microsphere200 acts as a lens that enhances the collection efficiency of the optical system.

The two microspheres are connected together. Light is passed by the optical combination of the two spheres.FIG. 2A shows optical ray tracing of the two microspheres. The ray originally starts at an angle θ relative to the vertical220. After passing through thelensing microsphere200, the ray continues at an angle φ′−θ″. If the lens is in water, the index of refraction of the water, n₁, is 1.3. Themicrosphere200 has an index of refraction, n₂, =1.59 (for polystyrene). Aphotodetector225 monitors for the proper fluorescence from themarked sphere210.

When themicrosphere pair199 is oriented relative to thephotodetector225 as shown inFIG. 2A, light passes through the flourescently-markedmicrosphere210 directly to thephotodetector225, and a relatively dim signal of themarked sphere210 is obtained.

FIG. 2B shows the microsphere pair oriented in alignment with theoptical collection axis220. In this situation, the fluorescence from the marked microsphere, or objective210 is enhanced by the lensing action of thelens200. The amount of collected light indicative of the marked lens is enhanced. This can be seen according to a geometric optics argument, as indicated inFIGS. 2C and 2D, which show schematic views comparing the magnitude of the signal received based upon orientation of the microspheres ofFIGS. 2A and 2B, respectively.

The angles of ray tracing are outlined in FIG.2A. The exit angle φ′−θ″ can be calculated as a function of the incident angle θ. Thefluorescent microsphere210 is approximated as a point particle located a distance δ from the lensing microsphere. Using geometry, it can be seen that
φ′=π−(π2θ′+φ)=2θ′−φ

Applying Snell's law at the top interface of the lensing microsphere:${\theta }^{″}={\sin }^{-1}\left(\frac{n_2}{n_1}\sin {\theta }^{\prime }\right)$

• • where n₂is the index of refraction of the lensing microsphere and n₁is the index of refraction of the surrounding medium (typically water). Applying Snell's law at the bottom interface gives${\theta }^{\prime }={\sin }^{-1}\left(\frac{n_1}{n_2}\sin \left(\theta +\varphi \right)\right)$

Then, direct substitution of equation (3) into equation (2), shows that
θ″=φ+θ

Using the law of sines, this can be rewritten as$\frac{\sin \left(\pi -\theta -\varphi \right)}{r+\delta }=\frac{\sin \theta }{r},$

• • and then explicitly find the angle φ as a function of r, θ, and δ:$\varphi \left(r,\theta ,\delta \right)={\sin }^{-1}\left(\frac{r+\delta }{r}\sin \theta \right)-\theta .$

Finally, the exit angle φ′−θ″ can be written in terms of the original angle θ, the radii of the two spheres, r, δ, and the indices of refraction, n₁and n₂.${\varphi }^{\prime }-{\theta }^{\mathrm{″\prime }}=2{\sin }^{-1}\left(\frac{n_1}{n_2}\sin \left(\theta +\varphi \left(r,\theta ,\delta \right)\right)\right)-\theta -2\varphi \left(r,\theta ,\delta \right).$

For δ<<t, φ<<θ. The exit angle is then given by${\varphi }^{\prime }-{\theta }^{\mathrm{″\prime }}=2{\sin }^{-1}\left(\frac{n_1}{n_2}\sin \theta \right)-\theta .$

Typical realizable values of n₁and n₂are for water, n₁=1.3 and polystyrene, n₂=1.59. For small θ, the equation above reduces to$\left(2\frac{n_1}{n_2}-1\right)\theta .$
This gives an exit angle of 0.64·θ for a ray entering at an angle θ. Since the exit angle is always less than the original angle, the lensing microsphere focuses rays from the fluorescent microspheres and enhances the optical signal.

The enhancement in the observed optical signal also depends on the numerical aperture of the objective. The numerical aperture (NA) is defined as NA=n sin θ₀, where θ₀is the collection angle. For the present objective (20x, 0.4 NA) in air θ₀=23.60. The equation shows that the focusing microsphere increases the angle of collection to 43.5°. This corresponds to an effective NA of 0.69. The epi-fluorescent intensity in proportional to NA⁴, so the intensity enhancement should relate (0.69/0.4)⁴≈9 times.

FIG. 3 shows a block diagram of the electronics of the system. Alight source300 shines light along anoptical axis305. Themicrosphere pair199 is located along thisoptical axis305. Light which shines through the microsphere pair impinges on aphotodetector310 which produces asignal315 indicative of the amount of incoming light. Thissignal315 is coupled to acontroller element320 such as a processor. The processor measures the signal amplitude of the flourescently-marked portion of the light. From this amplitude, the processor calculates either an orientation angle of thepair199, or more simply a signal indicative of the rate of change of that orientation angle.

The rate of change indicates the rate of rotation of thepair199.

The above has described one embodiment of these miniature lenses, but other applications are also possible.FIG. 4 shows the microlensing particle used in an optical scanning microscope. Themicrosphere lens100 is held within optical tweezers over asurface415 to be scanned. The lens is indexed by anindexer410 to scan the device across thesurface415. The surface can be illuminated by alamp420, causing light to reflect off the surface. Alternatively, the light fromlamp420 can cause fluorescence of the materials on thesurface415.

The light reflected from the surface, shown as425, produces anoutput430 which is collimated when the microsphere is directly above the surface area being imaged.

The microlens enhances the numerical aperture of theobjective440 of themicroscope438. This enables the microscope to have a high numerical aperture combined with a long working distance. Such a microscope avoids the usual trade off between light collecting capability (numerical aperture) and working distance.

In one mode, themicrolens100 can actually be smaller than the wavelength of light that is used. This allows the microscope to resolve at a resolution that is higher than the diffraction limit of the radiation.

Another application of the microlens is shown in FIG.5. Diode lasers are often small devices which produce a laser output over a very small scale. The laser output is often Gaussian.

A diode laser relies on two mirrors shown as500 and502 to form alasing cavity504. The present embodiment attaches microlens506 directly on theoutput mirror500. This helps collimate thelaser beam510. Moreover, since the laser itself is often on the order of size of 10 μm. a microscopic lens can help collimate almost all of the output light from the laser while minimally adding to the size of the laser.

FIG. 6 shows anoptical fiber600 using light collimated by a lens, to converge on thefiber end605. In this embodiment,microsphere lens100 is coupled directly onto the end of the fiber, and centered on the end of the fiber. The microsphere increases the effective numerical aperture and hence improves the coupling efficiency of the light.

In the embodiments ofFIGS. 5 and 6, the lens can be attached to the desired surface, using a biochemical glue such as avidin or biotin, to hold the lens in place. Alternatively, the lens could be properly positioned with optical tweezers, and melted or welded into place.

Other modifications are contemplated.

Claims (12)

1. An optical device comprising:

a spherical lensing element having a diameter of 10 μm or less, the spherical lensing element configured to collimate incident light to generate a collimated light beam; and an optical imaging element receiving the collimated light beam,

wherein the incident light is generated by a source element having a diameter of 10 μm or less that is in physical contact with the spherical lensing element, the diameter of the source element is smaller than the diameter of the of the lensing element.

2. The optical device ofclaim 1 wherein the incident light is generated by fluorescence of the source element.

3. The optical device ofclaim 1 wherein the optical imaging element is configured to detect an amplitude of the collimated light beam.

4. The optical device ofclaim 3 wherein the optical imaging element is configured to detect an angle of orientation of the linked source and lensing elements relative to the optical imaging element.

5. The optical device ofclaim 3 wherein the optical imaging element is configured to detect a rate of change of an angle of orientation of the joined source and lensing elements relative to the optical imaging element.

6. The optical device ofclaim 3 wherein the optical imaging element comprises a photodetector.

7. The optical device ofclaim 6 wherein the lensing element is configured to receive the incident light reflected from the surface.

8. A method of focusing light comprising:

collimating incident light with a spherical lensing element having a diameter of 10 μm or less, and

generating the incident light from a source element having a diameter of 10 μm or less in physical contact with the spherical lensing element, the diameter of the source element is smaller than the diameter of the lensing element.

9. The method ofclaim 8 wherein the incident light is generated by fluorescence of the source element.

10. A method of focusing light comprising collimating incident light with a spherical lensing element having a diameter of 10 μm or less, and

detecting an amplitude of the collimated light.

11. The method ofclaim 10 further comprising correlating the amplitude of the collimated light with an angle of orientation of the linked source and lensing elements relative to an optical imaging element.

12. The method ofclaim 11 wherein the correlation comprises determining a rate of change of an angle of orientation of joined source and lensing elements relative to the optical imaging element.

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